PROJECT SUMMARY: This is a re-submission for a National Institute of Environmental Health Sciences R21 award aiming to comprehensively evaluate digital auscultation and pulmonary function testing among Bangladeshi infants as innovative respiratory outcomes for future air pollution research in low-middle income countries (LMICs). Household air pollution (HAP) is the number one environmental cause of death worldwide and disproportionally affects the health of rural women and children in LMICs like Bangladesh. Particulate matter with an aerodynamic diameter <2.5 m (PM2.5) is an important indoor pollutant that is primarily generated by biomass fuel use during cooking, heating, and lighting. Elevated PM2.5 exposure has been associated with a substantially increased risk of child pneumonia mortality, the leading cause of infectious death in children globally, and childhood asthma incidence, the number one chronic lung disease among children worldwide. To date LMIC HAP research aiming to evaluate respiratory outcomes in children associated with PM2.5 exposure has focused on the acute endpoint of World Health Organization-defined pneumonia, a diagnosis known as poorly accurate and highly non-specific for studying pediatric respiratory health effects attributable to HAP. We aim to generate evidence supporting digital auscultation and pulmonary function testing as feasible, innovative, and diagnostically accurate pediatric respiratory health outcomes for inclusion in future LMIC HAP research within the rural communities most affected by HAP. To accomplish this overall goal we will conduct a longitudinal birth cohort study among 400 rural Bangladeshi pregnant women and their infants until the age of two months. For Aim 1 we will systematically evaluate lung sound recording quality by community health workers using a novel digital stethoscope during their care of rural Bangladeshi infants. We hypothesize that >90% of sounds will meet quality criteria, high interpretation agreement will be achieved between human listeners and also between automated computer analysis and humans, and that elevated prenatal PM2.5 concentrations will be associated with a higher incidence of abnormal digitally recorded lung sounds among infants. For Aim 2 we will create population reference values and evaluate the feasibility and validity of non-invasive, unsedated lung function testing of rural Bangladeshi two month old infants. We hypothesize that >90% of measurements will meet international validation criteria, infant lung function testing will be feasible, and that prenatal exposure to elevated PM2.5 concentrations will be associated with lower infant lung function. Successful completion of the research described in this application will dramatically advance the methodology for accurate assessment of acute and chronic child respiratory outcomes for future LMIC HAP research, and can also serve as crosscutting methods suitable for resource-rich settings and non-HAP research in LMICs.